Method for pneumatic flotation



Dec. 23, 1941. E. J. ELLIS ETAL 2,267,496

METHOD FOR PNEUMATIC FLOTA'IION Filed Aug. 10, 1938 2 Shee'ts-Sheet l zomum ELL /5 JOHN w. mMPL 1N Dec. 23, 1941. E. J. ELLIS ET 2 ,267,496

METHOD FOR PNEUMATIC FLOTATION Filed Aug. 10, 1958 2 Sheets-Sheet 2 OIL MTER C A T/ON/C REA GEN! DESL/MED FEED ENULSIFICI? FL GA TED 1 5 EPA RATQ R UNFLQA 11:0

Elva 00AM EDWARD'J-ELLIS (JOHN M PAHPL/N Patented Dec. 23, 1941 -2,zs7,m Mormon ron rm-zumanc nora'rron Edward]. Ellis and John w.

Fla., assignors to Southern ration, Baltimore, Md.,

ware

Pamplin, Bartow, Phosphate Corpoa corporation of Dela- Applicatlon August 10, 1938, Serial No. 224,209

6 Claims.

This invention relates to the separation of different kinds of minerals by pneumatic flotation and includes an improved method of concentra tion.

While we shall particularly describe our invention in connection with the separation of quartz sand from phosphate rock, the invention can be utilized with other materials that are amenable to separation by pneumatic flotation.

The apparatus employed in carrying out the improved method of separation is essentially a long shallow inclined launder with a smooth porous bottom or its equivalent which covers a compressed air chamber extending the length of the launder. In operation, a stream of fluid pulp, conditioned as for flotation, flows swiftly down the inclined launder in a shallow stream without substantial sedimentation or pooling, and without substantial agitation. As the air passes upwardly through the porous bottom the particles of the pulp that are amenable to flotation adhere to the air bubbles and are quickly lifted into the upper portion of the rapidly moving stream, while the remaining particles are carried along over the porous bottom. The upper parts of the pulp stream may then be skimmed 01f progressively under the momentum of the pulp stream itself by skimmers set at an angle to the line of flow and led out through the side of the launder and collected in separate receivers, while the material that is carried along the bottom of the stream discharges through the open end of the launder.

We will now proceed to explain the application of the principle of our invention to the separation of quartz sand from phosphate rock by floating off the sand, although the phosphate rock when suitably conditioned can be equally well floated out from the quartz sand. The phosphate material to which we apply our process,

by way of example, is Florida pebble phosphate washery waste, a low grade phosphatic material locally known as debris or recovery plant feed." This material, mostly finer than twenty mesh, consists mainly of quar sand, together with smaller amounts of phosphate rock (B. P. L.), clay, and slime. By slime is meant extremely fine particles of clay, and phophate in semi-colloidal suspension. The proportions of the constituents will vary in general as follows: phosphate rock 15-35%; sand 80-50%; and slime 0.55.0%.

It has heretofore been discovered by one of us that the quartz can be floated off from the tation cells, or on shaking tables, by the use of so-called cationic reagents, which have a preferential afllnity for the quartz particles and form weakly bonded coatings on them and render them floatable from the phosphate particles by adhesion to the air bubbles. These reagents are typified by the group of compounds known as quaternary ammonium salts that ionize in water. The quaternary ammonium compounds are among the best of the known frothing agents.

It has also been heretofore discovered by one of us that a relatively small amount of an inert oil, such as petroleum fuel oil, when introduced with the cationic reagent, will film the quartz particle, will reduce the amount of cationic reagent necessary to effect a complete separation, and will also eifect the separation of a somewhat coarser quartz particle. In the process of thus separating the sand from the phosphate rock, the pulp, having been-mixed with a suitable quantity of cationic reagent and oil, was treated on the conventional type of shaking table or in the conventional type of flotation cell to separate the quartz sand from the phosphate rock.

In carrying out our present process, we have discovered that, generally speaking, with the same reagents we can effect separation by the use of smaller amounts of the reagents specifled above, andin addition the relative capacity of our apparatus is much greater.

Referring to the drawings for a more complete disclosure of the invention:

Figure l is a plan view of the pneumatic flotation launder used in carrying out theprocess.

Figure 2 is a section on the line 2-2 of Figure 1.

Figure 3 is a fragmentary perspective view of the discharge end of the launder.

Figure 4 is a section on the line 44 of Figure 1.

Figure 5 is a diagrammatic view of the flowing pulp, showing the progressive removal of the upper layers of the pulp stream.

Figure 6 is a diagrammatic layout of a recovery unit.

Figure 7 is a vertical section of a preferred type of mixer for conditioning the feed with flotation agents.

Figure 8 illustrates a modified form of launder having riflles on the porous bottom for discharging unfloated material.

Figure 9 is a detail section on the line 9-9 of Figure 8.

The launder l is supported at the front or disphosphate rock in the. conventional types of 110- charg end y the pport 2 and at the upper end by'a support 3 that can be adjusted, as by the slot and bolt 4, to vary the inclination of the launder. The launder is divided by the longitudinal partition I into two compartments, the compartment 3 being the one in which separation takes place, and the compartment 1 being the one into which the floated portion is discharged. At the feed end of the compartment 8 is an air box 3 to which air under suitable pressure is supplied through the valved pipe 9. Running longitudinally of the compartment 6 is the partition l and the supports ll. Stretched across the partition Ill and secured to the supports II and the partition is the smooth porous bottom, here shown as of canvas material l2. Compressed air is fed through the pipe 9 into the air box 8, and flows through the two holes 13 into the two air boxes I4 and I, closed at their ends and underlying the canvas, and passes up through the canvas bottom in the form of finely disseminated streams.

The conditioned pulp to be treated is fed in a freely fluent state to the upper end of the launder through the spout l6. At the open discharge end of the launder is the hopper H for receiving the discharge from compartment 6, and the hopper l8 for separately receiving the discharge from compartment 1.

Extending transversely of the compartment 6 are the series of spaced skimmers IQ for skimming off the floated upper portion of the pulp. These are adjustable vertically, there being a slot 20 engaging a screw 2| at one end, and a slot 22 engaging a screw 23 at the other end. The discharge ends of the skimmers fit into notches 24 in the partition 5, and baflles 25 are attached to the skimmers to close the openings below the skimmers and prevent leakage. As the conditioned pulp flows down the inclined launder, the air under pressure passes up through the pores of the canvas in finely disseminated streams, floating off certain particles, forming a component of the pulp away from the remaining pulp components to the top without agitating the pulp in a way to impair substantially any collecting or frothing action involved in the flotation, where the upper stratum containing the flotation products are skimmed off under the momentum of the pulp stream itself by the skimmers and discharged into the compartment 1 where they flow out of the open discharge end of the launder into the collecting hopper Ill. The skimmers I! may be made of sheet metal and have a horizontal shelf-like portion 26 that widens, for example, from one inch at the upstream end to four inches at the downstream end, and a vertical partition part 21 about two inches high, at right angles to the part 26. These adjustable skimmers may be spaced, for example, about two and one-half feet apart beginning about three feet from the feed end, and extend across the width of the compartment 6 at an angle of about thirty-five degrees to the direction of flow.

In order to have adequate capacity, as well as to prevent blanketing the canvas by sedimentation of solid material from the pulp stream, the launder is set at an angle to the horizontal. In one type that was successfully used, the separating launder was twelve feet long, five inches wide, and one and one-half inches deep, with an inclination of about two inches per lineal foot, or about eight to ten degrees from the horizontal. From these dimensions, it will be seen that the pneumatic separator is a relatively long, shallow, narrow, inclined launder, with an open end for discharging the unfloated portion of the pulp. At the feed end of the launder, the conditioned pulp, containing from twenty to thirty per cent solids, was about one inch deep. As shown in Figure 5, the first skimmer 28 reduced the depth of the flowing pulp about one-quarter of an inch, the second skimmer 23 reduced it another quarter of an inch, and the third skimmer reduced it about one-eighth of an inch, leaving the pulp at the discharge end about three-eighths of an inch in depth. The amount of air forced through the porous bottom was about ten cubic feet per minute per square foot of porous bottom. The pulp velocity was of the order of one hundred to two hundred feet per minute.

To obtain good results as to separation, and at the same time maintain low reagent consumption by our process, it is desirable to accomplish both the mixing of reagents and feed, and separation of the conditioned quartz from the phosphate in as short a time as possible and with a minimum of attrition.

We have found it beneficial to emulsify the reagents in order to accomplish their mixing with the feed in as short a time as possible.

A type of mixer that has been found satisfactory consisted of a vertical cylinder seventeen inches high and eight inches in diameter with a canvas bottom through which air under onehalf pound pressure and at an estimated rate of sixty cubic feet per minute was added. The feed and reagents were fed to the mixer through a two inch standpipe that extended from six inches above the cylinder to within two inches of the canvas bottom. The feed rate was from about one to two tons per hour of phosphatic material in a pulp containing about sixty per cent solids. and the time of mixing was less than one minute.

Referring now to Figure 6, there is illustrated diagrammatically a plant layout for use in treating phosphate material that has been substantially deslimed. Into the emulsifier 3| are fed the cationic reagent, water, and oil in the proportions that are proper, and emulsification is there performed. The emulsifier discharges the emulsion through the pipe 32 into the covered hopper 33 where it is added to the deslimed feed from the spout 34, and conditioning takes place in the mixer 35. The mixer, as shown in Figure '7, is provided with a porous bottom 36, such as canvas, through which air from the valved pipe 31 is forced under pressure to mix the pulp. The feed passes down through the standpipe 38 and up between the standpipe and the outer shell 39 where it is mixed. After being mixed, the pulp overflows into the launder 40 and is discharged through the spout 4| into the spout 16 at the feed end of the launder I. Water from the pipe 42 may be mixed with the conditioned pulp before it enters the launder l.

Instead of skimming off the froth and other floated portions by intercepting the current, we may divert the unfloated portions to discharge ports along the side of the separating launder, permitting the floated portions to flow off through the open end of the separating launder. Such an arrangement is disclosed in Figures 8 and 9, in which the riffles 33 are secured to and overlie the canvas bottom and are set at an angle thereto, the unfloated minerals in the bottom of the launder being sluiced through the openings 44 in the side of the launder.

Our process, as applied to the separation of quartz from Florida phosphate rock, may be out- 2,207,400 3 lined as tgollowatw'l'hety raw material, which largely Immple 3 passes ugh en mesh, is deslimed. bullied with about forty per cent oi clear water, and t'11 1:' then gently and quickly mixed with an emulsion of a cationic reagent, an inert oil such as petro- Distribution, leum fuel oil, and water. A cationic reagent product Weight. Lon: BPL mm that may be used satisfactorily, as shown in the following tests, is manufactured by the Society BPL of Chemical Industry in Basle, Switzerland, and sold under the trade name of "Flotation Reagent 5x13352513 f}; 3;: 23:3: $13 K12 SKW, the exact composition of which is un- (1111mm known to us at present, but which is known to u 88 contain a quaternary ammonium salt as the effective reagent. There are other cationic re- Example 4 ,1 agents on the market'that are known to have Reagentsperlongtonofsolids, .4sib. oiKW. 3.511. offucloil, mm. the same property of floating quartz that will act equally well. After mixing the pulp and emulsion. the quartz sand has a fllm of oil and is ,33t"' rendered water-repellant while the phosphate Product 3mm fifi BPL Imoi. remains water-wet. The quartz can then be BPL 1M1. separated by flotation in our launder.

The following results were secured using a Fe mo am 6182 mo mo launder as heneinbefore described. The reagents z ggg 4 61 74 w 9 18 77 0 4 5 used were, BKW n tWO and -h f P cent Tailing(floated so: 1141 9114 s01 70 2110 0615 water solution, and twenty to twenty-two de- 5 gree Baum gravity fuel oil, fed together as an Example 5 emulsion to the mixer. DuPonts B 23, a commercial product comprising a mixture of sparingly soluble alcohols, was used part of the time as a frother. Nine gallons of clear water per minute was fed to the conditioned pulp as it flowed into the launder. The floated material was removed by three skimmers as hereinbefore described. It was estimated that forty per cent oi. the floated material was removed by the first skimmer, fifty per cent by the second, and ten per cent by the third.

The velocity of the flowing pulp was such that all of the floated material was removed in less than flve seconds after the pulp entered the launder, and most of it was removed in less than two seconds.

The following examples are illustrative of the results obtained in carrying out the process on washer tailings from the San Gully mine of the Southem Phosphate Corporation, Bartow, Florida:

Reagents per long ton of solids, oi KW, 3.7 lb. oi fuel oil, .09 lb.

Distribution, Weight, Long Product percent tons/hr BPL Insol.

BPL Insol.

Feed 100. 0 l. 15 29. 62. 82 100. 0 100. 0 COIl06ntl)Bt6 33.5 .39 71. 13.67 81.1 7.1

unilosted 'li iling (floated)- 66 5 76 8 88. 84 18. 0 92. 9

Reagents per long ton solids, .40 12.30! KW, 5.3 lb. of iucloil, .09 lb. oi

Distribution, Weight,

percent Long Product tons/h BPL Insol.

BPL Insol.

Feed

C o neentrats (unfloated).--.

Tailing (floated). l. 60 81. 50

Among the advantages of our invention may be mentioned the following:

The high velocity of the pulp stream due to the inclination and open discharge end of the launder enables the apparatus to easily handle relatively coarse material that may be in the feed. This is particularly advantageous where the valuable mineral is relatively coarser than the gangue and remains unfloated while the gangue is floated away. For instance, when the hereinabove referred to phosphatic matrial is concentrated in our pneumatic launder with the use of cationic reagents, the coarser particles as well as the finer phosphate particles pass through and discharge as a concentrate at the end of the launder.

The maintenance of a very shallow pulp stream 8 in our invention has certain definite advantages. The power required to furnish the air is low. The shallow pulp permits rapid flotation of the quartz sand as a fragile froth without the essential use of a frother. The coarser quartz particles, which, in general, are more difflcult to lift into the froth than the flner quartz particles, are easily removed because the air bubbles have only a short vertical distance in which to levitate them. It reduces the attrition of the particles due to the fact that the bed of pulp on the bottom of the launder is very mobile. Attrition between the particles or against moving parts produces slime, which slime consumes the cationic reagent and prevents the flotation of the quartz or causes excessive consumption of the reagents.

Our apparatus gives a rapid separation by flotation with a minimum of attrition. This is particularly advantageous for flotation of surfacetreated minerals when the beneficial eilects of such surface treatment are relatively unstable and pass off quickly or easily unless separation is eflected immediately after treatment. We have found that the fllming of quartz with the assistance of a cationic reagent is a treatment of this unstable character when a minimum amount of these reagents is used.

Since the pulp velocity through the launder is relatively high, 1. e. of the order of from one hundred to two hundred feet per minute, it prevents blanketing of the porous bottom and facilitates the quick removal of the floating froth and gives a large capacity to the launder.

While we have described the best method oi carrying out our process as applied to the pneumatic flotation of quartz sand from phosphatic material, we do not intend to so limit the process to these particular materials, but consider any similar materials that are amenable to pneumatic flotation as falling within the scope of our invention.

Other cationic reagents than those specified and which yield lipophiiic cations and hydrophilic anions in solutions in water may be employed, such as phosphonium or sulphonium salts. The inert oily material may be selected from a number of oils, tars, pitches, waxes, the essential characteristic being substantial insolubility in water.

Substances to promote frothing may be selected from a number of well known frothing agents, such as pine oils or tars, cresylic acid, frothing alcohols, bone distillates, etc.

From the above description, it will be seen that when treating mineral bearing material, such as phosphate debris, which is a mixture of particles of varying sizes, that the pulp must be sufliciently liquid to permit a fast flowing stream, so that the coarse particles along the bottom will be transported and promptly discharged from the launder, and so that the floated particles, especially the coarse ones, may be promptly skimmed off while they are in the upper part of the stream. It is difficult to levitate coarse particles and in view of the weak bond between the rising air bubbles and the coated coarse quartz particles, this separation is best effected in a shallow stream, where there will be less tendency for the air bubbles to separate from the quartz particles. Removal of the levitated particles by skimming permits not only removal of the particles in proximity to the surface of the stream but also permits removal of those particles being transported in the layer of liquid overlying the unfloated minerals. The passage of air through the porous bottom must be in the form of flnely disseminated bubbles and not as continuous jets or blasts which would cause undue commotion and lift unfloated minerals into the skimming zone where they would be caught and lost, in case the valuable mineral remains unfloated, or contaminate the concentrate in case the valuable mineral is floated. The horizontal shelf of the skimmer precludes descent of the particles once they have been caught.

It is to be understood that the above description and examples are by way of illustration and not of limitation, and the scope of the invention is to be determined by the appended claims We claim:

1. A process for separating mineral aggregate bles, flowing said pulp rapidly in a shallow stream downwardly over a relatively smooth. inclined surface without substantial sedimentation or pooling, passing flnely disseminated streams of gas upwardly through the downwardly flowing pulp stream and diverting to a separate receiver, under the momentum of the pulp stream itself, at least one stratum of the stream from the remainder of the flowing stream, to separate the floated from the unfloated particles.

2. A process for separating mineral aggregate containing particles of at least two components, which comprises forming a freely fluent pulp of the aggregate, conditioned for separation and containing a reagent which renders a component floatable from another by adhesion to air bubbles, flowing said pulp rapidly in a shallow stream downwardly over. a relatively smooth, inclined surface without substantial sedimentation or pooling, passing finely disseminated streams of gas upwardly through the downwardly-flowing pulp stream without agitating the pulp in a way to impair substantially any collecting or frothing action involved in the flotation; and diverting to a separate receiver, under the momentum of the pulp stream itself, at least one stratum of the stream from the remainder of the flowing stream, to separate the floated from the unfloated particles.

3. A process for separating mineral aggregate containing particles of at least two components, which comprises forming a pulp of the aggregate, conditioned for separation and containing about 20% to 30% solids and a reagent which renders a component floatable from another by adhesion to air bubbles, flowing said pulp in a shallow stream downwardly over a relatively smooth, porous, inclined surface, at a speed not substantially less than 100 ft. per minute without substantial sedimentation or pooling, passing finely disseminated streams of gas upwardly through said surface and through the pulp stream, and diverting to a separate receiver, under the momentum of the pulp stream itself, at least one stratum of the stream from the remainder of the flowing stream, to separate the floated from the unfloated particles.

4. A process for recovering phosphate concentrate from an aggregate of quartz and phosphate particles which comprises mixing with the aggregate, in conditioning it for separation, a reagent which renders particles of one of said species floatable from the other in an aqueous pulp by adhesion to air bubbles, forming a freely fluent pulp of the aggregate, flowing said pulp rapidly in a shallow stream downwardly over a relatively smooth, inclined surface .without substantial sedimentation or pooling, passing finely disseminated streams of gas upwardly through the pulp stream as it flows downwardly over said surface, and diverting to a separate receiver, under the momentum of the pulp stream itself, at least one stratum of the stream from the remainder of the flowing stream to separate the floated from the unfloated particles.

5. A process for recovering phosphate concentrate from an aggregate of quartz and phosphate particles which comprises mixing with the aggregate, in conditioning it for separation, a reagent which has a preferential aflinity for the quartz particles, forms weakly bonded coatings on said particles and renders them floatable from the phosphate particles by adhesion to air bubbles, forming a freely fluent pulp of the aggregate, flowing said pulp rapidly in a shallow stream downwardly over a relatively smooth, porous, inclined surface without substantial sedimentation or pooling, passing finely disseminated streams of gas upwardly through said surface and through the pulp stream, and diverting to a separate receiver, under the momentum of the stream itself, at least one stratum of the stream from the remainder of the flowing stream, to separate the floated quartz particles from the unfloated phosphate particles.

6. A process of recovering phosphate concentrate from phosphate washery waste containing phosphate and quartz particles which comprises mixing with the phosphate washery waste, in conditioning it for separation, a reagent which renders particles of one oi said species floatable from the other in an aqueous pulp by adhesion to air bubbles forming a freely fluent pulp of the aggregate, flowing said pulp rapidly in a shallow stream downwardly over a relatively smooth, inclined surface without substantial sedimentation, passing finely disseminated streams of gas upwardly through the pulp stream without agitating the pulp in a way to impair substantially any collecting or frothing action involved in the flotation, and diverting to a separate receiver, under the momentum of the pulp stream itself, at least one stratum of the stream from the remainder of the flowing stream, to separate the floated from the unfloated particles.

EDWARD J. ELLIS. JOHN W. PAMPLIN. 

